Investigate possilbe problems with CellGrid

[prock]

If you take a quick look at CellGrid? and how it's used you'll notice that Model owns it. If you ask Model for a CellGrid? by type it will clone a grid (if it finds it) and pass you a pointer to a new instance and adding the new instance to the end of it's list. The properties of the grid are cloned excluding the allow_diagonals property.

On a side note you'll notice also that the "m_allow_diagonals" property will always be the default because there is no way to modify it.

This ticket is to look at the current cell grid implementation and re-design/clean it up.

[prock]

(In [3549]) * Modified the owner of CellGrids?. They are now owned by Layer.

• Made Model more of a Factory class for CellGrids?. I'm not sure this is exactly what we should be doing but it does allow clients to add their own CellGrids?. Perhaps the best way to handle it would be to force the client to create their own grid a pass it to the Layer. refs #518

[prock]

(In [3638]) * undid some changes I made in r3539 that modified the owner of cellgrids. I decided that this wasn't a useful change so I'm reverting it until this ticket can be looked at in more depth. refs #518

[prock]

Moving this ticket to 0.3.4

[vtchill]

(In [3693]) reverted the changes in the layerdialog to reflect the reverted changes in the engine core dealing with cell grids. This fixes the exception being thrown when modifying layer properties. refs #518

[prock]

Moving to 0.3.5 as we are preparing to release 0.3.4